Reliable high performance drop generator for an inkjet printhead

Abstract

An inkjet drop ejection system comprises a combination of printhead components and ink, mutually tuned to maximize operating characteristics of the printhead and print quality and dry time of the ink. Use of a short shelf (distance from ink source to ink firing element), on the order of 55 microns, provides a very high speed refill. However, it is a characteristic of high speed refill that it has a tendency for being overdamped. To provide the requisite damping, the ink should have a viscosity greater than about 2 cp. In this way, the ink and architecture work together to provide a tuned system that enables stable operation at high frequencies. One advantage of the combination of a pigment and a dispersant in the ink is the resultant higher viscosity provided. The high speed would be of little value if the ink did not have a fast enough rate of drying. This is accomplished by the addition of alcohols or alcohol(s) and surfactant(s) to the ink. Fast dry times are achieved with a combination of alcohols, such as isopropyl alcohol with a 4 or 5 carbon alcohol or with iso-propyl alcohol plus surfactant(s). One preferred embodiment of a short shelf (90 to 130 microns), ink viscosity of about 3 cp, and surface tension of about 54 provides a high speed drop generator capable of operating at about 12 KHz. Reducing the shelf length to about 55 microns, in combination with rotating the substrate at an angle to the scan direction, permits maximum drop generator operation as high as about 20 KHz. As a consequence of employing pigment-based inks, high optical densities are realized, along with excellent permanence (no fade and better waterfastness), and good stability. The combination of preferred ink and pen architecture provides good drop generator stability.

What is claimed is: 
     
       1. An inkjet drop ejection system comprising: (a) a substantially rectangular substrate having a top surface and an opposing bottom surface, and having a first outer edge along a periphery of said substrate and a second outer edge along said opposite periphery of said substrate, said substantially rectangular substrate having two opposed edges that are shorter than said first and second outer edges;   (b) a nozzle member having a plurality of ink orifices formed therein, said nozzle member being positioned to overlie said top surface of said substrate;   (c) first and second pluralities of ink ejection elements formed on said top surface of said substrate, each of said ink ejection elements comprising a firing element in a vaporization chamber and being located approximate to an associated one of said orifices for causing a portion of ink to be expelled from said associated orifice as said inkjet drop ejection system is moved along a scan direction, said first plurality of ink ejection elements arranged in a first array along said first outer edge and said second plurality of ink ejection elements arranged in a second array along said second outer edge;   (d) an ink reservoir for holding a quantity of ink;   (e) a fluid channel, communicating with said reservoir, leading to each of said orifices and said ink ejection elements, said fluid channel allowing ink to flow from said ink reservoir, around said first outer edge of said substrate and to said top edge of said substrate so as to be proximate to said orifices and said ink ejection elements;   (f) a separate inlet passage defined by a barrier layer for each vaporization chamber connecting said secondary channel with said vaporization chamber for allowing high frequency refill of said vaporization chamber;   (g) said separate inlet passage for each vaporization chamber having pinch points formed in said barrier layer to prevent cross-talk and overshoot during high frequency operation;   (h) circuit means for transmitting firing signals to said ink firing elements at a maximum frequency greater than 9 KHz;   (i) said inkjet drop ejection system forming a part of a color set of comprising at least one ink, said ink comprising at least one colorant in an aqueous vehicle; and   (j) a support surface under said two shorter edges of said substrate, each support surface including a projection extending beneath said substrate to support said substrate while allowing ink to flow unimpeded around said first outer edge.   
     
     
       2. The inkjet drop ejection system of claim 1, wherein said firing elements are arranged in a staggered configuration along said substrate such that adjacent firing elements are located at different shelf lengths along said edge thereof. 
     
     
       3. The inkjet drop ejection system of claim 2, wherein said separate inlet passage for each vaporization chamber additionally has peninsulas. 
     
     
       4. The inkjet drop ejection system of claim 2, wherein every other one of said separate inlet passages has a peninsula. 
     
     
       5. The inkjet drop ejection system of claim 1, wherein said firing elements are arranged along said substrate at substantially identical shelf lengths along said edge thereof, said substrate rotated with respect to said scan direction to compensate for timing delays between adjacent nozzles. 
     
     
       6. The inkjet drop ejection system of claim 5, wherein said substrate is rotated by an amount given by (φ=arcsine((v*t)/D), where v is scan velocity of said inkjet drop ejection system, t is time delay between firing two adjacent ink ejection elements, and D is distance between adjacent nozzles. 
     
     
       7. The inkjet drop ejection system of claim 1, wherein said vaporization chambers are substantially rectangular. 
     
     
       8. The inkjet drop ejection system of claim 1, wherein said vaporization chambers are substantially circular. 
     
     
       9. The inkjet drop ejection system of claim 1, wherein a group of said vaporization chambers in adjacent relationship form a primitive in which only one vaporization chamber in said primitive is activated at a time. 
     
     
       10. The inkjet drop ejection system of claim 1, wherein said colorant comprises a pigment. 
     
     
       11. The inkjet drop ejection system of claim 10, wherein said pigment is black. 
     
     
       12. The inkjet drop ejection system of claim 10, wherein said pigment is selected from the group consisting of cyan, yellow, and magenta pigments. 
     
     
       13. The inkjet drop ejection system of claim 10, wherein said pigment has a particle size within the range of about 20 to 99 nm. 
     
     
       14. The inkjet drop ejection system of claim 10, wherein said pigment has a particle size within the range of about 100 to 125 nm. 
     
     
       15. The inkjet drop ejection system of claim 10, wherein said pigment has a particle size within the range of about 126 to 200 nm. 
     
     
       16. The inkjet drop ejection system of claim 10, wherein said ink further includes a pigment dispersant. 
     
     
       17. The inkjet drop ejection system of claim 16, wherein said pigment dispersant is an acrylic. 
     
     
       18. The inkjet drop ejection system of claim 16, wherein said pigment dispersant is a non-acrylic. 
     
     
       19. The inkjet drop ejection system of claim 16, wherein said pigment dispersant is a block polymer. 
     
     
       20. The inkjet drop ejection system of claim 16, wherein said pigment dispersant is a non-block polymer. 
     
     
       21. The inkjet drop ejection system of claim 20, wherein said pigment dispersant is selected from the group consisting of random, star, and graft polymers. 
     
     
       22. The inkjet drop ejection system of claim 16, wherein said dispersant comprises at least one hydrophilic molecule covalently bonded to said pigment. 
     
     
       23. The inkjet drop ejection system of claim 16, wherein said vehicle includes a dry time component. 
     
     
       24. The inkjet drop ejection system of claim 23, wherein said dry time component comprises at least two alcohols in an amount sufficient to provide said ink with a dry time of about 15 to 45 seconds on typical office copier papers. 
     
     
       25. The inkjet drop ejection system of claim 23, wherein said dry time component comprises at least one alcohol and at least one surfactant in amounts sufficient to provide said ink with a dry time of about 15 to 45 seconds on typical office copier papers. 
     
     
       26. The inkjet drop ejection system of claim 1, wherein said colorant comprises a dye. 
     
     
       27. The inkjet drop generator of claim 26, wherein said dye is a black dye. 
     
     
       28. The inkjet drop ejection system of claim 27, wherein said dye is Reactive Black 31. 
     
     
       29. The inkjet drop ejection system of claim 27, wherein said dye is Projet Fast Black 2. 
     
     
       30. The inkjet drop ejection system of claim 27, wherein said dye is selected from the group consisting of Food Black 2, Direct Black 168, Direct Black 19, and Mobay Special Direct Black (SP). 
     
     
       31. The inkjet drop ejection system of claim 26, wherein said dye is selected from the group consisting of cyan, yellow, and magenta dyes. 
     
     
       32. The inkjet drop ejection system in claim 1, wherein said vehicle contains at least one cosolvent in an amount of about 2 to 60 wt % of said ink. 
     
     
       33. The inkjet drop ejection system of claim 32, wherein said cosolvent is a polyethylene glycol. 
     
     
       34. The inkjet drop ejection system of claim 32, wherein said cosolvent is selected from the group consisting of diethylene glycol, glycerol, triethylene glycol, N-methyl pyrrolidone, tetraethylene glycol, 1,4-butanediol, 1,2-pentanediol, and 1,5-pentanediol, present in an amount of about 3 to 15 wt % of said ink. 
     
     
       35. The inkjet drop ejection system of claim 32, wherein said vehicle includes 2-pyrrolidone in the range of 8 to about 10 wt % of said ink. 
     
     
       36. The inkjet drop ejection system of claim 32, wherein said vehicle comprises 2-pyrrolidone in the range of about 3 to up to 8 wt % of said ink. 
     
     
       37. The inkjet drop ejection system of claim 1, wherein said ink has a viscosity within the range of about 1.2 to 2.5 cp. 
     
     
       38. The inkjet drop ejection system of claim 1, wherein said ink has a viscosity within the range of about 2.6 to 3.4 cp. 
     
     
       39. The inkjet drop ejection system of claim 1, wherein said ink has a viscosity within the range of about 3.5 to 8 cp. 
     
     
       40. The inkjet drop ejection system of claim 1, wherein said ink has a surface tension within the range of about 30 to 49 cp. 
     
     
       41. The inkjet drop ejection system of claim 1, wherein said ink has a surface tension within the range of about 50 to 58 cp. 
     
     
       42. The inkjet drop ejection system of claim 1, wherein said ink has a surface tension within the range of about 59 to 65 cp.